This probably sounds awful but hear me out. DSD7 is with us full time for the summer. She lives abroad with her mum and her school dates are different, so she's with us for about another month. DP ex is a different religion to us, DP converted while married to her so is technically the same religion, but doesn't practice.
DSD doesn't eat certain foods while with DP ex for religious reasons. She also doesn't eat certain combinations of foods together. DP ex has always wanted us to stick to these dietary requirements when she's with us, which of course I respect.
DP takes zero responsibility for mealtimes when DSD is here. He will occasionally cook for the kids when she's not here, but when she is he expects me to take on the mental load of planning things she can eat and our other kids will also eat. DDs are fussy eaters and a lot of the meals they will happily eat are things DSD can't, and aren't easy to adapt without having to make two separate meals. DSD is very overweight currently so I don't want to just put a ready meal in front of her, which DP would do most nights if I didn't cook.
AIBU to want him to take more responsibility? He has actually followed this diet so has a better idea of what to feed her than I do anyway.